In many instruments used to perform geodetic measurements, particularly digital theodolites with integrated angle sensing and distance measuring systems, such as described in U.S. Pat. No. 4,205,385, there are employed gravity-related sensing devices which maintain a datum reference with respect to the attitude of the primary, vertical axis of the instrument.
One such a sensing device, described in U.S. Pat. No. 4,077,132, utilizes a capacitive pick-up system which includes a pendulously-suspended weight member which serves as an electrode common to a blanced pair of capacitors. In order to provide a high level of sensitivity in the device therein described, the suspension system comprises a number of relatively narrow flexible straps which support this mobile electrode. However, while these strap members provide a ready response to minute displacement of the reference axis, due to their flexibility they unfortunately render the sensing device susceptible to damage as a result of the rough handling which is often encountered during the course of a surveying project.
A device which is sensitive enough to register slight deviations from a base reference attitude, yet is able to withstand reasonably severe physical shocks or jarring, has thus long been needed in the field of geodetics and other real-world environments. The present invention provides such a versatile mislevel sensing device.